Electrostatic precipitator system

ABSTRACT

An improved electrostatic precipitator device capable of significant size reduction having flat parallel plates consisting of an ionizing corona discharge portion as a unitary structure which is utilized to effectuate precipitation of entrained particles from an air stream onto the surface of a plurality of associated collection members, as an air stream containing entrained particles is cleaned in passing through the precipitator device. The ionizer discharge portion of the unitary structure comprises a plurality of substantially uniformly spaced apart sharp electrical conductive protrusions directed to alternate sides of the unitary structure; thereby forming a uniform ionization region with a parallel portion of the collector extending the full length of the ionizer. The remainder of each of the unitary structure functions as a passive electrode which cooperates with the remaining portion of the collector to form highly concentrated electrostatic fields therebetween for enhanced collection efficiency with minimum re-entrainment of the particles to be collected.

United States Patent Gourdine et al.

[451 Dec.5,-1972 [54] ELECTROSTATIC PRECIPITATOR SYSTEM [72] lnventors:Meredith C. Gourdine, West Orange; Howard A. Sayers, Clifton, both ofNJ.

[73] Assignee: Gourdine Systems, Inc., Livingston,

221 Filed: May 15, 1970 21 Appl.No.: 37,714

[58] Field of Search ..55/136, 137, 138, 139,142,55/l43,145,154,l50,152, 124,126,146

[56] References Cited UNITED STATESPATENTS 1,888,606 11/1932 Nesbit..55/152 X 2,255,677 9/1941 Penney .55/138 X 2,275,001 3/1942 Anderson55/137 X 2,490,979 12/1949 Palmer 55/138 X 2,969,127 1/1961 Cook..55/126 3,172,747 3/1965 Nodolf ...55/l26 X 3,191,362 6/1965 Bourgeois..55/138 x 3,271,932 9/1966 Newell ..55/138 X 3,412,530 11/1968 Cardiff..55/143 X 3,422,600 l/l969 Chamberlain ..55/126 3,511,030 5/1970 Hallet al. ..55/138 X 3540.191 ll/l97l) Herman ..55/138 X FOREIGN PATENTS ORAPPLICATIONS 611,137 10/1948 GreatBritain ..55/137 627,068 7/1949GreatBritain ..55/136 Primary Examiner-Dennis E. Talbert, Jr.-

Attorney-Brumbaugh, Graves, 'Donohue and Raymond [57] ABSTRACT Animproved electrostatic precipitator device capable of significant sizereduction having flat parallel plates consisting of an ionizing coronadischarge portion as a unitary structure which is utilized to effectuateprecipitation of entrained particles from an air stream onto the surfaceof a plurality of associated collection members, as an air streamcontaining entrained particles is cleaned in passing through theprecipitator device. The ionizer discharge portion of the unitarystructure comprises a plurality of substantially uniformly spaced apartsharp electrical conductive protrusions directed to alternate sides ofthe unitary structure; thereby forming a uniform ionization region witha parallel portion of the collector extending the full length of theionizer. The remainder of each of the unitary structure functions as apassive electrode which cooperates with the remaining portion of thecollector to form'highly concentrated electrostatic fields therebetweenfor enhanced collection efficiency with minimum re-entrainment of theparticles to be collected.

12 Claims, 6 Drawing Figures 18 5O TO 34 PATENTEDBEB 51912 3. 704, 572sum 1 0F F/G Z INVENTORS MEREDITH C. GOURDINE HOWARD A. SAYERS ATTORNEYELECTROSTATIC PRECIPITATOR SYSTEM BACKGROUND OF THE INVENTION In theprior art, electrostatic precipitators for the removal of entrainedparticles from air streams have employed upstream ionizer chambers inwhich the particles entrained in the air stream are electrostaticallycharged, followed by one or more separate downstream collection chamberscontaining collector plates upon which the charged particles areprecipitated during the air cleaning process. The ionizer electrodesmost widely and usually used for such precipitators consist of aplurality of very fine (small-diameter) wires, spacedapart and spacedbetween relatively widely spaced nondischarging electrodes, commonlyknown as attractor electrodes. The non-discharging attractor electrodeshave been either curved towards or away from the wires, or substantiallyflat, plate surfaces. In many cases, the flat plates are preferred forthe nondischarge electrodes, since they are simpler, less expensive andeasier to assemble and clean.

Still other arrangements have been employed, which utilize parallelplates in the collection region of the precipitator having polarities ofappropriate sign to adjacent plates. Such typical arrangements aredisclosed in U.S. Pat. Nos. 2,662,608 and 3,181,285. In both of thesereferenced patents, the ionization region for charging particlesentrained in an incoming air stream is separated from the collectionregion, which consists of a plurality of collector electrodes disposedin the path of the air stream with opposite polarities imposed uponadjacent collector electrodes. The primary distinction between thedevices in the cited references is the arrangements in the ionizer. InU.S. Pat. No. 2,662,608, the ionizer includes a series of longitudilystrung fine wires, while in U.S. Pat. No. 3,181,285, the ionizer is asingle steel needle element positioned on the center line of the airinlet tube which functions as the attractor electrode.

The present invention overcomes several obvious disadvantages of theprior art arrangements, one of which arises from the fact that theionization regions and the precipitation (collection) regions are inseparate chambers. Another disadvantage occurs as a result of thecharged particles precipitating out onto the surrounding walls of theattractor electrode, that is, the walls of the attractor electrodeadjacent to the ionizer electrode in areas which are not accessible forcleaning. Precipitation of particles on the attractor walls in theionizer section tends to reduce the ionization level in the ionizerregion, which in turn, reduces the effectiveness and efficiency forcharging the entrained particles in the air stream. In addition, owingto the non-uniform distribution of precipitated particles onto the wallsof the attractor, the uniformity of corona discharge along the length ofthe corona wires will be non-uniform, which in turn, leads tonon-uniformity of charge imparted to the particles.

Still another disadvantage arises from the discovery that when theprecipitator device is constructed with rather narrow spacing betweenthe corona wires and the attractor electrode, significant electricalarcing or shorting between the two electrodes may occur from thenon-uniform deposition of particles on the attractor walls or from beingdeposited on the corona wires. The occurrence of such arcingsubstantially reduces the efficiency of operation and, in many cases,when continuous shorting occurs, it may cause the precipitator to becometotally inoperative.

Another disadvantage of having the ionizer and the collection chambersseparated, as is the case in the prior art, arises from the fact thatthere is a difference in electric field patterns in the transitionregion between the ionizer region and the upstream end of the collectorelectrodes. In various cases the electrodes in the collector region mayhave polarities or potentials different from that of the ionizerelectrodes. Such differences may tend to create electric fieldconditions in the transition region, which may often cause the chargedparticles to act in an undesirable and unpredictable manner, and therebycause non-uniformity of collection in the specific regions designatedfor such collection. The exact nature of these undesirable effects arenot clearly understood; however, the adverse effects of theiroccurrences have been observed and have been found to be objectionablefor the manufacture of commercially acceptable and reliable apparatus.

Still another apparent disadvantage of the prior art arrangement ofhaving the ionizer and collection chamber separated arises from the factthat such arrangements may cause the precipitator to be larger in sizethan may be desired or required to handle a preselected volume of air tobe cleaned. More specifically, in certain applications for example, in ahome kitchen range hood air cleaner utilized for cleaning the air in akitchen, which has become polluted from the cooking process, it has beenfound for many years to be uneconomical and also requires too much spacein the kitchen area to make it feasible to employ such large size priorart precipitators as a means for removing such air pollutants assmoke,.grease particles, and odor from the kitchen environmental air,solely because of the large physical size requirements for such purposeswith prior art devices. In addition, it is well recognized that suchtwo-stage systems are incapable of effectively removing both submicronsmoke, grease particles, and odors in a single-unit. This is apparentlyso because the two-stage units are'handicapped in not being able toadequately handle large size particles.

SUMMARY OF THE INVENTION In accordance with the present invention, theair cleaning precipitator device is constructed such that the ionizationand the collector regions comprise what may be termed as a continuoussystem, without a transition region between such functional chambers.More specifically, in one embodiment of the present invention theprecipitator comprises at least one unitary substantially flat platemember, essentially consisting of an ionizer electrode section,extending toward the upstream end of the precipitator and a passiveelectrode section, extending from the ionizer section toward thedownstream end of the precipitator. For each unitary plate member thereis positioned on opposite sides thereof a substantially parallel andco-extensive collector electrode, having an upstream portion thereofwhich extends past the ionizer electrode on opposite sides thereof inthe direction opposite to the incoming air stream. In the region betweenthe upstream end of the collector electrodes, adjacent to the ionizerthere is formed a corona discharge, whereby the entrained particles inthe air stream are charged.

The ionizer and passive electrodes are at the same electrical potentialwith respect to ground and polarity, while the collector electrodes areat a different electrical potential with respect to ground and polaritythan the corona and passive electrodes. In many instances the collectorelectrodes are at ground potential. These differences in polarities andpotential cause a corona discharge and electrostatic fields to beformed, respectively, between the ionizer and the upstream end of thecollector and between the passive electrode and the remainder of thecollector for enchanced collection efficiency and to substantiallyreduce particle re-entrainment.

In addition, it has been found that precipitators operated andconstructed in accordance with the present invention are capable ofprecipitating particles of both large and small (submicron) sizes,produced during the process of cooking foods. Still further, it has beenobserved by olfactory or smelling tests, that the odor levels producedduring cooking processes are significantly reduced. A completeunderstanding of these observations can not be readily explained;however, it is believed that the close proximity of the ionization andcollection regions in the precipitator enables more efficient chargingand collection of these large size particles or the agglomeration ofsmall particles to which gaseous odor attach and are removed. This hasnot heretofore effectively been done.

A further explanation of the precipitation process is based upon thebelief that the collection of both large and small particles is in partdue to turbulence created in the ionizer region which is evidenced by anenhancement of the corona wind produced therein.

In another embodiment of the invention the unitary ionizer and passivecollector electrodes are each constructed in the form of unitarystructures in an interleaved manner. In the embodiment the combinationionizer and passive electrode structure is disposed within theprecipitator in a fashion so as to avoid possible collection ofparticles thereon and thereby reducing, if not eliminating, theoccurrence of shorting out of the combined ionizer and passive electrodestructural member.

Another important feature of the present invention arises from the factthat a precipitator device may be constructed in a significantlysmaller-size volume unit, while still being capable. of handling aslarge a volume of air to be cleaned of pollutants as that of the priorart two-chamber devices. Still further, the unitary combinationstructure for an ionizer and passive electrode is adaptable tomultiple-stage arrangements in a minimum amount of space to add greaterair cleaning efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS being utilized as a component of aventilator precipitator system;

FIG. 2 is a diagramatic cross-section, illustrating a top view of anembodiment of the invention;

FIG. 3 is a diamgramatic cross-sectional view taken along line 33 ofFIG. 2, illustrating a side view;

FIG. 4 is a diagramatic cross-sectional view taken along line 4-4 ofFIG. 3, illustrating a back view;

FIG. 5 is a diagramatic cross-section, illustrating another embodimentof the invention; and

FIG. 6 is a diagramatic cross-sectional view taken along line 66 of FIG.5, illustrating a side view.

DESCRIPTION OF REPRESENTATIVE EMBODIMENTS In FIG. 1, a representativeembodiment of an electrostatic air cleaning precipitator constructed inaccordance with the present inventionis included as a component deviceof a ventilator air cleaning precipitator system. The precipitatorsystem 10, includes first and second filters 12 and 14, a blower fan'16, and a precipitator device 18, having an associated sump 20, forcollecting liquids. The first and second filters, the fan andprecipitator device, are disposed along a path 22 of an incoming airstream, illustrated as a pollutant air source 24, containing entrainedparticles and odors to be removed. Such entrained particles may be inthe form of dust, grease, steam, smoke, pollen, and the like, many ofwhich may be of the submicron size.

Also included in the system 10 is an electrical source of alternatingcurrent (A.C.) power 26, push-button interlock switches 28 and 30,respectively, for interconnecting with a direct current (DC) powersupply 32 and fan 16. The DC. powersupply 32, is connected toprecipitator device 18, through a convenientcircuit disconnect 34, alongconductor 36, while the precipitator is grounded by conductor 38, andthe power supply 32 is grounded by conductor 31.

The operation of the system is initiated by closing the switch 30 toconnect A.C. source. 26 to fan 16. When energized, the fan drawspollutant air 24 into the system along path 22, through the first andsecond filters l2 and 14. It should be noted that the filters are notabsolutely required for suitable operation but'may be preferred forcertain applications. The partially filtered air is then blown into theinlet end of the precipitator l8, and is exhausted out through theoutlet end thereof after having been cleaned. The manner in which theprecipitator 18 is constructed and operates will be discussed in greaterdetail with reference to FIGS. 2-4.

Referring now to FIGS. 2-4, wherein like characters in each view aregiven the same reference designations, there is shown the precipitator18, which includes four insulator frame members 40-46, connected to forma rectangular support frame 48. Within the walls of the frame 48 are aplurality of parallel disposed spaced apart elements, essentiallycomprised of alternately spaced conductive substantially flat collectorplate members 50, which are electrically interconnected by groundingbridge wire 52 (see FIG. 4) a plurality of unitary plate members 54,each having an ionizer electrode 56 at the upstream and and a passiveelectrode 58 extending from the ionizer electrode 56 to the downstreamend. The upstream end of the device is adjacent to the incoming air,while the downstream end is near the exhaust air outlet. Each of theunitary plate members 54 is electrically interconnected by a bridgingconductive member 60. i

Referring specifically to FIG. 4, it can be seen that each unitary platemember 54 is electrically insulated from each collector electrode by aseries of grooved insulation support members 62, which extend the fulllength of the frame 48 (also see FIG. 3). These insulative supportmembers 62 are positioned at both the top and the bottom of the frame48, adjacent frame members 40 and 44. However, it should be recognizedthat these insulative support members 62 may be included as an integralpart of adjacent frame members 40 and 44.

Referring now to FIGS. 2 and 3, the physical configuration of theionizer electrode 56 is shown in greater detail. As shown in thedrawings, a saw-toothed edge member 64, forms the active coronadischarge tips or points for the electrode. In contrast to the fine wireor single tip corona needle most commonly utilized in the prior art, thepresent ionizer electrode is provided with multiple corona dischargepoints, for which the corona discharge may advantageously be maintained.Upon closer inspection with reference to FIG. 2, it can be seen that thesaw-blade configuration of the ionizer electrode has a set, that is,alternate teeth of the sawblade member point to opposite sides of thecorona discharge region.

The unique-feature of the set in the corona teeth or tips of the coronaelectrode 64 enable the corona discharge to be substantially uniformlydistributed in a fixed manner along the entire length of the structureand corona discharge region. In general, it is believed that theindividual teeth of the saw-blade structure are capable of substantiallyindependent operation, and, thereby providing a structure of novelfunctional capabilities. in contrast to the single fine-wire electrodecommonly employed in the prior art, the saw-blade configuration 64 ofthe present invention provides several advantages. Firstly, it providesmultiple needle points for independent high current paths, such that anyentrained particles which may be collected thereon may be burned offreadily by high currents drawn by the points of the teeth. Secondly, theneedle points are staggered from point to point, such that substantiallyfixed uniform corona discharge exists along the entire length on eitherside thereof when negative corona is utilized whereas, if the coronaelectrode was a fine wire the corona discharge therealong when negativecorona is utilized would not always be in fixed positions, but wouldvary in their position depending on whether or not there was a build-upof impurities on the wire, thereby causing a significant degradation ofperformance.

Thirdly, as illustrated in FIG. 2, the ends of the needle points arelocated outward of the sides of the plate members 54 so as to be closerto the collector electrodes 50 than any other point on the plate members54. This prevents or greatly deters the creation of corona conditionsbetween impurities settling on downstream areas of the plate members 54and the opposed collectors 50, and thereby further ensures properionizer performance.

In conclusion, the precipitator device 18 may be considered completed bythe presence of a grounding shim 66, which is shown in FIG. 3, as beingconnected to conductor 38, and then to ground potential. The groundingshim 66 is connected to all of the collector electrodes 50, so as toplace them at ground potential with respect to the polarity of theunitary member electrodes 54, which are connected to another polaritywith respect to ground by conductor 36, which is connected to the DC.power supply 32. The DC. power supply is also grounded on one side. Thepolarity of the ionizer may be either positive or negative with respectto ground for operation. However, in practical operation of theprecipitator, it has been found that the use of a negative potential ispreferred.

In operation, the precipitator device 18, in the representativeembodiment of FIGS. 2-4, has the unitary members 54, including theionizer 56 and the passive electrode 58, at a negative potential withrespect to ground potential and the collector electrodes 50, which, asnoted, are connected to ground potential by means of shim 66 andconductor 38.

Such connections produce a negative corona discharge in the upstreamportion of the device between the saw-blade teeth section 64 of theionizer 56 and the upstream end of collector electrode 50. Between thepassive electrode 58 and the remainder of the collector electrodes 50,there is produced a strong electric field on the non-corona dischargetype.

The incoming pollutant air 24 carrying both large and small particlesand odors, which were not filtered out by the first and second filters,enters the corona discharge region adjacent to the saw-blade teeth 64,where they pick-up negative charge from ions in the corona discharge,either by diffusion charging or electric field charging. In general, thelarger particles acquire their charge by electric field charging, whilethe smaller particles, such as submicron particles, acquire their chargeprincipally by diffusion charging.

It is noteworthy to observe that diffusion charging is known to occurmore readily when there is corona wind such as that generated by thesaw-blade teeth ionizer in the present invention which causes turbulencein the ionization region. With the saw-blade arrangement of the presentinvention, it is believed that greater corona wind is generated thanheretofore known in compact precipitators. Thus, high efficiency in thepresent device is caused in part by the corona wind. The turbulencecaused by such corona wind can cause an increase in the residence timeof the particles in the ionization region and an increase in theparticle size due to agglomeration resulting from the presence ofturbulence. Both of these effects will result in a much higher chargeper particle level on those particles entering the collection region ofthe device. The above mentioned turbulence can also cause an increase inparticle collection in the collection region of the device due to thetransport of charged particles to the collector walls as a result ofwhat may be termed large scale" turbulence.

Referring now to FIGS. 5 and 6 there is shown another embodiment of theinvention wherein the precipitator 18 has disposed therein a unitarystructure 70, including a plurality of combination ionizers 56 andpassive electrodes 58, and a unitary structure 72, in cluding aplurality of collector electrodes 50 forming an interleaving arrangementtherebetween. The unitary structure 70 is disposed within theprecipitator 18 by at least two stand-off electrical connectors 74 whichare supported by a housing enclosure 76 of the precipitator. Connectedto one of the connectors 74 is a cable 77, including the conductor 36,for applying a DC.

potential to the combined ionizer and passive electrode as discussedhereinabove. The remainder of the device, which is metal, including thecollector electrode structure 72, may be connected to ground potentialby the conductor 38. Also shown in FIG. is a deflection baffle 78disposed in the upstream end of the precipitator l8 and a sump as anintegral component of the precipitator 18 with a plurality ofgravity-flow apertures 80 opening into the sump 20 for permitting theflow of liquids from the precipitation region to the sump. Forconvenience the sump 20 is in the form of a drawer, is slidablyremovable by pulling a knob 82, and is guided along support guidegrooves 84.

In FlG. 6 the relative space relationships of the elements of theprecipitator 18 may be seen more clearly. Baffle 78 may be deflected atan angleto the flow of air through the device, and has been disposedwith respect to the ionizer 56 and passive electrode 58 to prevent anyair from flowing along a path indicated by a curved broken-line arrow88. This arrangement insures that no entrained airborne particles arecollected on top of the unitary structure 70, where they may causeshorting between structure 70 and the enclosure 76, which is at groundpotential while the structure 70 may be at high negative potential.

The electrical operation of the precipitation shown in H68. 5 and 6 isessentially the same as that discussed hereinabove with respect to otherembodiments. However, it should be noted that the illustratedarrangement has the very important advantage of eliminating thepossibility for shorting between the elements which may occur readily ifthere are conductive particles in the pollutant air source.

Thus, it can be readily appreciated that the present invention hasseveral additional advantages over prior art precipitator arrangements.The most noticeable one being its ability to collect particles of allsizes more effectively and efficiently in a smaller package. Anotheradvantage of the invention is the elimination of the two-chamberprecipitator arrangements, which enable the device to be builteconomically and compactly, in contrast to prior art devices.Precipitators in accordance with the present invention have been built,

tested, and compared with data covering existing commercialpreciprtators. The results of several .comparrsons are set forth belowin a table:

Commercial Capacity in Thruput in Precipitator Cubic Foot Frontal CubicFoot/ Example Per Minute Area Min/Square Inch 1 1400 21%"Xl7fi" 3.86 22800 2lV4"X36%" 3.58 3 800 I6 l/l6"X ll ll/l6" 4.20 4 1200 27%" X lllfi" 3.66 5 2000 31%"X l67/l6" 3.86 Present Invention 600 5%" X 5%"2l.60

From the foregoing data illustrating comparisons, it is believed thatthe precipitator, in accordance with the present invention, is capableof cleaning approximately five times as much air per unit time per unitcross-sectional area as prior-art commercial air cleaning apparatus.

The foregoing would certainly support the belief that the presentinvention is capable of greater efficiency per unit frontal area and isadaptable to compactness in packaging in its construction.

Still another advantage may be derived from the present invention,namely, that of making the precipitator a multiple-stage device byplacing two or more of the unitary plate members 54 in series, such thatthe upstream end of the passive electrode is far enough removed from thenext succeeding ionizer sawblade element 64 not to interfere with thecorona discharge to be produced with such positioning. It is obviousthat under certain conditions, it may be highly desirable to utilizesuch a multiple-stage precipitator, such as, for example, where greaterair volume capability is required along with minimum volume and size ofprecipitator device. For example, the efficiency of the precipitator maybe increased by staging the unitary plate members in series along theflow path of air while capacity in terms of cubic inches of flow perminute (CFM) may be increased by adding units in parallel to the flowpath of the air stream.

Finally, the simplicity of construction of the present invention offersanother advantage for economy of manufacture for commercial use. v

It will be understood by those skilled in the art that theabove-described embodiments are intended to be merely exemplary, in thatthey are susceptable to modification and variation without departingfrom the spirit and scope of the invention. For example, it will beapparent that the precipitator of the present invention may be adaptedfor high-pressure oil separation systems, vacuum cleaners and othernumerous air pollution control devices. All such modifications andvariations, therefore, are intended to be included within the scope andspirit of the invention, as defined by the appended claims. A

What is claimed is:

1. An electrostatic precipitator for removing particles entrained in afluid stream comprising;

a housing having a fluid inlet and a fluid outlet and formingtherebetween a flow path for the fluid stream;

at least one plate electrode member positioned transversely of the flowpath and extending ina direction generally parallel to the direction offlow from an upstream end adjacent the fluidinlet to a downstream endadjacent the fluid outlet;

a plurality of pointed members spaced along the upstream end of eachplate electrode member and extending upstream therefrom at an acuteangle to the longitudinal centerline of the electrode member, saidpointed members being symmetrically disposed on opposite sides of saidlongitudinal centerline;

a plate collector electrode positioned on either side of each plateelectrode member in generally parallel relation thereto, each collectorelectrode having an upstream end located upstream of the pointed membersof the adjacent plate electrode member and a downstream end locatedadjacent the downstream end of said plate electrode member; and

means for establishing a potential difference between each plateelectrode member and the adjacent collector electrodes productive of (1)a corona discharge between each pointed member and the opposed region ofeach collector electrode that is directed in substantial part againstthe direction of flow and (2) a nondischarging precipitation fieldbetween the region of each plate electrode member downstream of thepointed members and the opposed region of each collector electrode.

2. An electrostatic precipitator as defined in claim 1 wherein aplurality of said plate electrode members are positioned within the flowpath in spaced-apart generally parallel relation, and said plurality ofelectrode members are connected together at one edge thereof to form afirst unitary plate assembly in parallel array.

3. An electrostatic precipitator as defined in claim 2 wherein thecollector electrodes positioned on opposite sides of said plateelectrode members are connected together at one edge thereof to form asecond unitary plate assembly in parallel array.

4. An electrostatic precipitator as defined in claim 3 wherein saidpotential difference establishing means includes means for electricallygrounding said collector electrodes and means for applying a negativepotential to said plate electrode members.

5. An electrostatic precipitator as defined in claim 1 furthercomprising sump means for receiving and storing particles precipitatedfrom the fluid stream.

6. An electrostatic precipitator as defined in claim 5 wherein eachplate electrode member and collector electrode is vertically disposedwithin the housing; and

the housing further includes a member forming a lower boundary for theflow path, said member having formed therein a plurality of apertures,and sump means positioned below said member for receiving therethroughparticles precipitated from the fluid stream.

7. An electrostatic precipitator as defined in claim 6 wherein thecollector electrodes are supported in parallel spaced relation to theassociated plate electrode members by the lower boundary forming member.

8. An electrostatic precipitator as defined in claim 6 wherein:

a plurality of plate electrode members are positioned within the flowpath;

said plurality of electrode members are connected together at theirupper edges so as to form a first unitary plate assembly in parallelarray; and

the collector electrodes associated with said plurality of plateelectrode members are connected together at their lower edges by thelower bounda-- ry forming member so as to form a second unitary plateassembly in parallel array, the plates of the first and secondassemblies being interleaved.

9. An electrostatic precipitator as defined in claim 1 wherein theupstream ends of said pointed members extend outward of the sides of theassociated plate electrode member so as to be positioned closer to theadjacent collector electrodes than any other part of the electrodemember.

10. An electrostatic precipitator as defined in claim 1 whereinalternately spaced ones of said pointed members are disposed on oppositesides of the longitudinal centerline of the electrode member.

11. An air cleaning system for treating environmental air in a buildingenclosure, including means for flowing the environmental air through thesystem, a mechanical air filter at an upstream location within thesystem and an electrostatic precipitator for electrostatically removingparticulates from the air at a downstream location within the system,wherein the improvement comprises;

at least one plate electrode member positioned within the precipitatorto extend from a upstream end adjacent the precipitator inlet in adirection generally parallel to the direction of flow to a downstreamend adjacent the precipitator outlet, said upstream and downstream endsof each plate electrode member thereby extending transversely of thedirection of flow;

a plurality of pointed members spaced along the upstream end of eachplate electrode member and extending upstream therefrom at an acuteangle to the longitudinal centerline of the electrode member, saidpointed members being symmetrically disposed on opposite sides of saidlongitudinal centerline;

a plate collector electrode positioned on either side of each electrodemember in generally parallel relation thereto and having an upstream endlocated upstream of the pointed members of the adjacent electrode memberand a downstream end adjacent the downstream end of said electrodemember; and

means for establishing a potential difference between each electrodemember and the adjacent collector electrodes productive of (1) a coronadischarge between each pointed member and the opposed region of eachcollector electrode that is directed in substantial part against thedirection of flow and (2) a nondischarging precipitation field betweenthe region of each electrode member downstream of the pointed membersand the opposed region of each collector electrode.

12. An electrostatic precipitator as defined in claim 1 1 wherein saidpotential difference establishing means and said means for passing airthrough the system are independently energizable.

1. An electrostatic precipitator for removing particles entrained in afluid stream comprising; a housing having a fluid inlet and a fluidoutlet and forming therebetween a flow path for the fluid stream; atleast one plate electrode member positioned transversely of the flowpath and extending in a direction generally parallel to the directIon offlow from an upstream end adjacent the fluid inlet to a downstream endadjacent the fluid outlet; a plurality of pointed members spaced alongthe upstream end of each plate electrode member and extending upstreamtherefrom at an acute angle to the longitudinal centerline of theelectrode member, said pointed members being symmetrically disposed onopposite sides of said longitudinal centerline; a plate collectorelectrode positioned on either side of each plate electrode member ingenerally parallel relation thereto, each collector electrode having anupstream end located upstream of the pointed members of the adjacentplate electrode member and a downstream end located adjacent thedownstream end of said plate electrode member; and means forestablishing a potential difference between each plate electrode memberand the adjacent collector electrodes productive of (1) a coronadischarge between each pointed member and the opposed region of eachcollector electrode that is directed in substantial part against thedirection of flow and (2) a nondischarging precipitation field betweenthe region of each plate electrode member downstream of the pointedmembers and the opposed region of each collector electrode.
 2. Anelectrostatic precipitator as defined in claim 1 wherein a plurality ofsaid plate electrode members are positioned within the flow path inspaced-apart generally parallel relation, and said plurality ofelectrode members are connected together at one edge thereof to form afirst unitary plate assembly in parallel array.
 3. An electrostaticprecipitator as defined in claim 2 wherein the collector electrodespositioned on opposite sides of said plate electrode members areconnected together at one edge thereof to form a second unitary plateassembly in parallel array.
 4. An electrostatic precipitator as definedin claim 3 wherein said potential difference establishing means includesmeans for electrically grounding said collector electrodes and means forapplying a negative potential to said plate electrode members.
 5. Anelectrostatic precipitator as defined in claim 1 further comprising sumpmeans for receiving and storing particles precipitated from the fluidstream.
 6. An electrostatic precipitator as defined in claim 5 whereineach plate electrode member and collector electrode is verticallydisposed within the housing; and the housing further includes a memberforming a lower boundary for the flow path, said member having formedtherein a plurality of apertures, and sump means positioned below saidmember for receiving therethrough particles precipitated from the fluidstream.
 7. An electrostatic precipitator as defined in claim 6 whereinthe collector electrodes are supported in parallel spaced relation tothe associated plate electrode members by the lower boundary formingmember.
 8. An electrostatic precipitator as defined in claim 6 wherein:a plurality of plate electrode members are positioned within the flowpath; said plurality of electrode members are connected together attheir upper edges so as to form a first unitary plate assembly inparallel array; and the collector electrodes associated with saidplurality of plate electrode members are connected together at theirlower edges by the lower boundary forming member so as to form a secondunitary plate assembly in parallel array, the plates of the first andsecond assemblies being interleaved.
 9. An electrostatic precipitator asdefined in claim 1 wherein the upstream ends of said pointed membersextend outward of the sides of the associated plate electrode member soas to be positioned closer to the adjacent collector electrodes than anyother part of the electrode member.
 10. An electrostatic precipitator asdefined in claim 1 wherein alternately spaced ones of said pointedmembers are disposed on opposite sides of the longitudinal centerline ofthe electrode member.
 11. An air cleaning system for treatingenvironmenTal air in a building enclosure, including means for flowingthe environmental air through the system, a mechanical air filter at anupstream location within the system and an electrostatic precipitatorfor electrostatically removing particulates from the air at a downstreamlocation within the system, wherein the improvement comprises; at leastone plate electrode member positioned within the precipitator to extendfrom a upstream end adjacent the precipitator inlet in a directiongenerally parallel to the direction of flow to a downstream end adjacentthe precipitator outlet, said upstream and downstream ends of each plateelectrode member thereby extending transversely of the direction offlow; a plurality of pointed members spaced along the upstream end ofeach plate electrode member and extending upstream therefrom at an acuteangle to the longitudinal centerline of the electrode member, saidpointed members being symmetrically disposed on opposite sides of saidlongitudinal centerline; a plate collector electrode positioned oneither side of each electrode member in generally parallel relationthereto and having an upstream end located upstream of the pointedmembers of the adjacent electrode member and a downstream end adjacentthe downstream end of said electrode member; and means for establishinga potential difference between each electrode member and the adjacentcollector electrodes productive of (1) a corona discharge between eachpointed member and the opposed region of each collector electrode thatis directed in substantial part against the direction of flow and (2) anondischarging precipitation field between the region of each electrodemember downstream of the pointed members and the opposed region of eachcollector electrode.
 12. An electrostatic precipitator as defined inclaim 11 wherein said potential difference establishing means and saidmeans for passing air through the system are independently energizable.